The present invention relates to methods of diagnosing, prognosing or treating diseases or disorders in which elevated levels of Aβ protein, including Aβ1-42 are prevalent. In particular, the present invention relates to methods of diagnosing, prognosing or treating a mood disorder such as a major or minor depressive disorder or dysthymia attributed to reduced levels of Aβ protein, including Aβ1-42, found particularly in body fluids including whole blood, blood cells, serum, plasma, urine and CSF. The invention also relates to the treatment of these disorders and methods of identifying subjects who may respond positively to such treatment by administering an agent that either prevents production of Aβ, prevents aggregation of Aβ fibrils, that increases the degradation or clearance of Aβ or that prevents or interferes with Abeta-induced neurotoxicity.
